This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2009-180685 filed in Japan on Aug. 3, 2009, the entire contents of which are herein incorporated by reference.
The present invention relates to a technology that is applied in an image forming apparatus using an electrophotographic method, such as a copying machine, a facsimile, or a printer, and more specifically to a fixing apparatus and an image forming apparatus including the fixing apparatus.
Generally, in an image forming apparatus using an electrophotographic method, an electrostatic latent image is formed on the surface of a photosensitive drum. Then, the electrostatic latent image on the surface of the photosensitive drum is developed using toner, and a toner image is thereby formed on the surface of the photosensitive drum. Thereafter, the toner image is transferred from the photosensitive drum onto recording paper, the recording paper is heated and pressed, and thus the toner image is fixed onto the recording paper.
A fixing apparatus fixes a toner image onto recording paper. In the fixing apparatus, recording paper is sandwiched in a nip region between a hot roller and a pressure roller, which form a pair, and is transported. Accordingly, the recording paper is heated and pressed by the rollers, so that toner on the recording paper is heated and melted so as to be fixed.
The method of sandwiching recording paper in the nip region between the pair of the hot roller and the pressure roller as described above is suited to speed up the fixing process because the temperature of the hot roller can be easily maintained at a constant fixing temperature.
In the fixing apparatus as described above, in order to retain the width of the nip region between the hot roller and the pressure roller and stably maintain the nip region, by covering the rollers with an elastic layer, the elastic layers of each roller are pressed against each other and deformed.
However, since the pressure between the rollers is great, when the fixing apparatus is not used and the rollers are in a stopped state for a long time, the elastic layers of the rollers are left deformed and sometimes unable to return to their original shape, thus forming a depression in the elastic layers of the rollers.
For this reason, a mechanism for applying and cancelling pressure between the hot roller and the pressure roller may be provided. That is to say, in an operating state, the hot roller and the pressure roller are pressed against each other by a biasing force of a spring, and in a non-operating state, the hot roller or the pressure roller is displaced in a direction away from the other against the biasing force of the spring to reduce the pressure between the rollers to a lower value or to zero.
For example, JP2006-162996A and JP 2005-10218A disclose such technology.
Incidentally, there is a problem in that if residual toner in solid form is sticking in a gap between an outer circumferential face of the pressure roller and a leading edge of a detachment claw, as the pressure roller rotates, the residual toner clogs up and accumulates in the gap between the detachment claw and the pressure roller, obstructs the rotation of the roller, and consequently damages the pressure roller, for example. This problem leads to dirt on paper.